The Breeding System and Distribution of <i>Tetrahymena pyriformis.</i>*

Abstract

SUMMARY. Seven hundred twenty samples of water from 46 states and the province of Ontario, Canada, were collected and examined for Tetrahymena pyriformis. Thirty‐four hundred clonal cultures of the ciliate were isolated from the 154 (21%) positive samples and grown axenically in peptone medium. The breeding behavior of strains from these 154, sources was investigated by mixing clonal cultures in various combinations. Eight sources yielded selfing strains and 52 yielded strains capable of mating only in certain combinations. Thirty new mating types in seven new non‐interbreeding varieties were discovered. Ninety of the 154 collections yielded non‐conjugating strains. Fifty of these proved to be amicronucleate. Distribution of variety 2 organisms was the most widespread; 22 collections from 11 states and Ontario, Canada, were obtained. Variety 3 was collected 14 times from seven states. Other varieties were found less often. The ciliate was found about as often in running as in standing water, but certain varieties were found predominantly in one or the other habitat.